Comparison of laser energy absorption between Thulium and Ytterbium laser for PBF-LB of magnesium WE43

Additive manufacturing of magnesium WE43 components, especially in powder bed fusion of metals using a laser beam (PBF-LB/M), offers promising applications for bioresorbable, patient-specific implants. However, significant challenges persist in PBF-LB/M of magnesium. The primary hurdle is strong processing emissions, resulting from magnesium’s low boiling point (1110 °C), which is exceeded in the high-temperature zone of the laser beam during PBF-LB-processing. High peak temperatures result from the energy input required to melt the oxides and alloying elements (4 wt.-% Yttrium and 3 wt.-% rare earth elements). The literature indicates that at room temperature, the laser absorption in magnesium at a wavelength of 1070 nm in magnesium is very low (6.6 %) and that it could be improved by a factor of ≈ 3 to 19.5 % at 1958 nm.
This study investigates the potential of a novel thulium laser source with a wavelength of 1958 nm by studying the absorption coefficients and heat-up rates in magnesium WE43 powder. While optical measurements regarding the reflectivity of a broadband light source on WE43 powder showed a slight 3.1 % increase in absorption, diffuse reflectance infrared fourier transform spectroscopy measurements showed an increase in reflectivity compared to an aluminum reference in the 1958 nm range of 8.2 %. Furthermore, heat-up rate experiments revealed a 4.7-fold improvement under thulium laser radiation. These findings underscore the potential of thulium lasers to overcome current limitations in magnesium alloy processing for PBF-LB/M.